This paper presents results of the direct shear tests on pre-fractured specimens from Rurikfjellet Formation, Svalbard, Arctic Norway. It also evaluates the risk of shear failure along pre-existing fractures due to possible over pressure. Rurikfjellet Formation is composed of clay-rich shale and is part of the cap rock for the proposed CO₂ storage pilot at Svalbard. Shear properties of the cap rock system are of great importance for the integrity of the reservoir beneath. Three specimens from Rurikfjellet Formation were subjected to direct shear test. Results of the experiments showed that the peak friction coefficient was slightly higher than the residual coefficient. Shear stiffness of the specimens varied between 19 and 21 MPa/mm determined from secant method and between 26 and 32 MPa/mm determined from tangent method. The specimens showed slight dilation in the very initial phase of shearing but exhibited strong compression with increased displacement (and normal stress). This indicates that a slip along fractures in Rurikfjellet shale may be governed by compression which in turn implies self-sealing of fractures that may occur during a shear displacement. Evaluation of fracture reactivation under stress conditions close to that of the current situation at Svalbard showed that there is a safety margin of about 4 to 5 MPa overpressure before a failure may occur along the critically oriented fractures. Overall, the measured compression behaviour and the estimated safety margin for Rurikfjellet shale suggest that this unit may act as a good seal for the proposed CO₂ storage reservoir.

本文介绍了对来自北极挪威斯瓦尔巴特群岛的鲁里克菲耶特地层的预破裂标本进行的直接剪切试验的结果。它还评估了由于可能存在的过大压力而沿既有裂缝发生剪切破坏的风险。Rurikfjellet地层由富含粘土的页岩组成，是提议的CO ₂盖层的一部分斯瓦尔巴特群岛的存储飞行员。盖层岩石系统的剪切特性对于下面储层的完整性非常重要。来自Rurikfjellet地层的三个标本经过直接剪切测试。实验结果表明，峰值摩擦系数略高于残余系数。试样的抗剪刚度在通过割线法确定的19至21 MPa / mm之间和通过切线法确定的26至32 MPa / mm之间变化。试样在剪切的最初阶段显示出轻微的膨胀，但随着位移（和法向应力）的增加而显示出强烈的压缩。这表明沿Rurikfjellet页岩裂缝的滑动可能受压缩控制，这反过来又意味着在剪切位移过程中可能发生裂缝的自密封。在应力条件下进行的裂缝再活化评估接近于斯瓦尔巴特群岛目前的情况，结果表明，在沿临界取向裂缝发生破坏之前，存在约4至5 MPa超压的安全裕度。总体而言，测得的Rurikfjellet页岩压缩行为和估计的安全裕度表明，该单元可作为拟议CO的良好密封。_2个储水库。